The present invention relates to an integrated module for solid oxide fuel cell (xe2x80x9cSOFCxe2x80x9d) systems comprising an afterburner, a heat exchanger and a fuel processor.
As many remote power customers use natural gas or propane, these are obvious choices for SOFC fuel in remote power generation systems. As well, many other applications exist for fuel cell systems such as residential cogeneration and automotive uses. SOFCs have the advantage of easily being able to use hydrocarbon fuels through fuel processing methods including steam reforming, partial oxidation and autothermal reforming. As fuel processing of hydrocarbons occurs at or near SOFC operating temperatures, thermal integration of both the fuel processor and stack is desired.
Steam reforming is a method that realizes a high overall system efficiency and provides the stack with a hydrogen-rich fuel. Therefore, it is desirable to provide a SOFC system that uses steam reforming of a hydrocarbon fuel.
It would be advantageous if a module for use with a SOFC system would effectively: 1) completely oxidize the fuel remaining in the SOFC stack anode exhaust gas using the stack cathode exhaust gas or other air, and 2) directly utilizes the heat produced by oxidation of the anode exhaust gases to preheat and prereform all or a desired portion all of the hydrocarbon/water fuel mixture being fed to the SOFC stack, using a suitable catalyst, and 3) directly heat the incoming (to SOFC stack) cathode air.
An integrated module for use in a solid oxide fuel cell (xe2x80x9cSOFCxe2x80x9d) system is disclosed which combines several functions into one unit. In one embodiment, the integrated module oxidizes the fuel cell stack anode exhaust using the stack cathode exhaust or other air, preheats and prereforms (processes a percentage of, or completely) the incoming hydrocarbon/water mixture using a suitable catalyst to provide a hydrogen and carbon monoxide rich stream for the fuel cell anode, and also further heats the air destined for the SOFC cathode.
In one aspect, the present invention comprises a SOFC system including a fuel cell having a fuel intake, an air intake, a cathode exhaust and an anode exhaust, and comprising an integrated module comprising an afterburner, a fuel processor and a heat exchanger, wherein: (a) said afterburner comprises an intake connected to the anode exhaust, or anode and cathode exhausts, and an igniter; (b) said heat exchanger comprises an intake connected to an air supply and an exhaust connected to the air intake of the SOFC wherein the heat exchanger is thermally coupled to the afterburner; and (c) said fuel processor comprises an intake connected to a fuel/water supply, a fuel reforming catalyst, and an exhaust connected to the fuel intake of the SOFC wherein the fuel processor is thermally coupled to the heat exchanger and/or the afterburner.
The afterburner burns the unused fuel in the SOFC stack exhaust. The heat produced by the afterburner is exchanged by the heat exchanger to preheat the air stream into the SOFC stack. The fuel/water stream is also preheated and prereformed in the fuel processor which also uses heat from the afterburner. The fuel processor comprises an effective catalyst so that steam reformation of the hydrocarbon fuel may take place as it passes through the fuel processor.
In one embodiment the afterburner is comprised of a tubular combustion chamber and an igniter. The combustion chamber is encircled by a high temperature heat air exchanger for transferring the combustion heat to the incoming air and fuel/water mixture. The heat exchanger is itself encircled by the fuel processor. Therefore, the integrated module may be comprised of a tubular core, a middle shell which contains the heat exchanger and an outer shell which contains the fuel processor.